1. Field
One or more embodiments of the present invention relate to a system, method and medium correcting brightness of an image, and more particularly, to a system, method and medium correcting brightness of an image and capable of correcting brightness of an acquired image to a target brightness.
2. Description of the Related Art
In order to correct brightness of an image acquired by an image acquisition apparatus such as a camera or a camcorder, the difference between a current brightness of the acquired image and a target brightness of the acquired image is generally treated as an error. If the error exceeds a predetermined level, an exposure time and a gain are adjusted so that the current brightness of the acquired image can be adjusted to approach the target brightness.
In this case, the image acquisition apparatus performs a feedback loop in which the brightness of the acquired image is repeatedly corrected through the adjustment of the exposure time and gain until the error continuously caused by the difference between corrected brightness of the acquired image and the target brightness comes within the predetermined level.
When the brightness of the acquired image is repeatedly corrected until it becomes the target brightness, a correction value, used in the repeated corrections, may be set high so that the brightness of the acquired image reach the target brightness in a short period of time. However, with such large correction values, there is a risk that the corrected brightness of the acquired image will overshoot the target brightness, thereby causing oscillation. Consequently, system stability can be undermined. On the other hand, if the correction value is set too low for system stability, a time-consuming feedback loop becomes necessary.
Therefore, as determined by the present inventors, a method of correcting the current brightness of an image to a target brightness in a short period of time without causing oscillation is desirable.
Japanese Patent Publication No. 2003-125285 discusses a technique of storing information regarding the relationship between an exposure time of a camera and the brightness of an image in a database (DB) and referring to the stored information when necessary. Thus, this technique avoids the cycle of feedback control and its time-consuming control process. However, not all information regarding all possible relationships between the exposure time of the camera and the brightness of the image can be stored in the DB due to the huge quantity of necessary relationships. In addition, after data of a certain point is stored in the DB, the remaining points whose data is not stored must be inferred, e.g., through data interpolation. In addition, here, the relationship between the exposure time of the camera and the brightness of the image also varies according to the model of camera. Hence, the relationship is limited to a particular camera and does not have generality and flexibility. As a result, a separate DB must be implemented for each camera model.